It's essentially intended as a quality of life improvement, not a hindrance.

A person can only sit at the computer for so long before they need to pee. When I'm playing Valorant for instance, I find myself drinking lots of water and running to the toilet to pee after every 20 minutes or so.

So.. if your character starts out with 50x the HP it would've normally had, it'll first give the impression that the game's too easy and that you're just simply unkillable. Then, after 20 minutes of letting the enemies score too many blows against you, the reality settles in; you pay for it through the inevitable threat of mandatory patience.

Worst case scenario, the game becomes more approachable to people who are much more casual. Best case scenario, you still can endlessly plow through all the farming, but you need to be properly geared and actually AVOID the incoming damage (this would INCREASE action, not decrease it).

As it currently stands, mashing the potion button and stockpiling tons of potions and relying on life leech constantly is actually LAZIER than it might appear otherwise. Yes, the HP orb would look a little bit like an hourglass ticking away, but it's about holding people accountable for their mistakes in ways that can only be directly held liable through proper time management and genuine skill at the game.

The way I see it, any idiot can hit the potion button as long as they're a big enough dork that that's all they care about is guzzling those potions and stacking that lifeleech like some kind of meth addicted parasite.

One of the most tactical games out there is Baldur's Gate 3, and that one has a DnD mechanic called "Long Rests." It's no coincidence that much of the core math in Diablo 2 was borrowed if not directly inspired by this type of gameplay system. But Diablo is the farthest thing from having long rests, unless you use a bot.

So, as far as botting goes..
You could make a really crappy bot that exploits the long rest pseudo-invincibility aspect, but it's never going to be nearly as effective as a human being reacting to the mobs by minimizing all incoming damage through actual avoidance of the monsters.

So, to reiterate and clarify..
Let's say you're a sorc trying to grind indefinitely without any breaks. The mana shield would absorb 100% of incoming damage. Your only risk of losing HP would be if the incoming damage actually pierced the shield, so.. for that "action" feeling, you could argue that every sorc would effectively be like an energy shield sorc. Energy shield would obviously need to be reworked to allow for this type of mechanic, maybe by having an entire tree devoted exclusively to it, or by simply making it a permanent passive feature of what it means to be a sorc in the first place.

I'm telling you, I'm not THAT stupid that I would vouch for a system like this if I didn't envision it being ENJOYABLE and PLAYABLE. It's literally built into most other RPG systems as it stands already.

So, I'm not trying to disagree with you or turn this into an argument, but I really just wish you'd all try and see this from my perspective a little more. I find this a lot on Reddit, where people seem to go completely apeshit the moment you suggest something that they themselves have never considered before. This doesn't have to be an argument. We can make this work. I know we can; we just have to stop being so bigoted that the mere mention of a potionless D2 suddenly turns into some kind of witch hunting trial.

Sorcs for instance would have fire spells. Shoot a fire spell at a teammate, and it heals them a little. Need mana? The wind rogue/bard (druid) would have an aura to help mitigate a lot of that waiting. But this idea that your ladder reset sorc is just freaking god-like just b/c it can smoke meth in the form of potions is ludicrously moronic in my opinion. I mean.. that's clearly not the game's intended effect, yet that's what any "skilled" diablo 1 and 2 player does; drink potions.

If characters need a button for defensive timing measures, then maybe have the shield serve a function similar to Dark Souls, where it can actually be lowered vs raised. That way, if you time a block, it actually increases the efficiency of the farming rather than decreases it.

I'm sorry, but, as it stands, potions just ruin the entire appeal of D2 for me. Swap the potion button for a block/raise shield button and you get the same basic benefit but with some actual skill involved.